Recent Advances in Generation and Detection of Orbital Angular Momentum Optical Beams-A Review

Abstract

Herein, we have discussed three major methods which have been generally employed for the generation of optical beams with orbital angular momentum (OAM). These methods include the practice of diffractive optics elements (DOEs), metasurfaces (MSs), and photonic integrated circuits (PICs) for the production of in-plane and out-of-plane OAM. This topic has been significantly evolved as a result; these three methods have been further implemented efficiently by different novel approaches which are discussed as well. Furthermore, development in the OAM detection techniques has also been presented. We have tried our best to bring novel and up-to-date information to the readers on this interesting and widely investigated topic.

Keywords: computer-generated holograms; diffractive optic elements; metasurfaces; optical waveguide; orbital angular momentum; spatial light modulator.

Figure 1

The number of papers related to the “Orbital angular momentum” topic searched in the Scopus database for the years 2000–2021.

Figure 2

Methods to generate light with OAM: (a) Shift in the OAM order by illuminating a 3D element with the laser light of different wavelengths [58]; (b) OAM generator via CGH [59]; (c) Schematic of the OV beam generator from MS [60]; and (d) The schematic illustration of the OV beam generator on the embedded multi-WG [61].

Figure 3

Elements of singular optics: (a) SPP. Reprinted with permission from ref. [36]. Copyright 1994, Elsevier; (b) spiral axicon; (c) spiral zone plate; (d) OV autofocusing optical element; (e) fork grating; (f) curved fork grating; and (g) grating for OV hyper-geometric laser beams generation.

Figure 4

Optical system for generation of vector OV beams by a combination of DOEs and anisotropic crystals: a He-Ne laser emitting linearly polarized light which was expanded using an objective (L1), a quarter-wave plate (QWP) was utilized to alter the linearly polarized beam into the circularly polarized beam, the diffractive optical element (DOE) generates OV Laguerre-Gaussian modes which are focusing by a lens (L2) into a c-cut CaCO₃ crystal, cylindrically polarized beams (with radial or azimuthal polarization) are imaging by a lens (L3) at CCD array and analyzed by a polarizer (P). Reprinted with permission from ref. [115]. Copyright 2017, Elsevier.

Figure 5

(a) The fabricated MS and its experimental setup with a WG probe in the near field chamber [126]. Radiation forms of the MS: (b) x-polarization, OAM mode l_x = +1 [126]; and (c) y-polarization, OAM mode l_y = −2 [126].

Figure 6

(a) Graphical design of all-fiber focused OV beam generator [141], (b) SEM image of the nanoimprinted KSZP microstructure with topological charge l = −1 [141], and (c) focal spot profiles acquired from FDTD simulation (top row), experimental measurement (middle row), and the measured coaxial interference forms (bottom row) [141].

Figure 7

The integrated photonic emitter: (a) The graphical illustration [145]; (b) the micrograph [145]; and (c) the SEM image of the manufactured device [145].

Figure 8

(a1,a2) Schematic of two single grating (with period of Λ₁ and Λ₂, respectively) superimposed into multiple-beat modulated device [151]. An unfolded view of resulting the three beats device (a3) [151]. The far-field patterns of the two-beat grating device: (b) 1508.1 nm, topological charges combination +1 and −1; (c) 1518.9 nm, topological charges combination 0 and −2; and (d) 1530 nm, topological charges combination −3 and −1 [151]. The near-field pattern is showing in (e), and the well-defined spiral interference fringe existed at appropriate locations is showing in (f) [151].

Figure 9

(a) The graphical image of the OV beam generator, (b) (b1–b4), the basis of the holographic grating on WG. The acquired OV beams by the holographic gratings with different sizes. The intensity and phase distributions are shown in the upper row and down row of the figures, (c–f) consistent to the holographic gratings with a constant width d = 1.5 μm but different lengths b = 1, 1.4, 1.8, 2.2 μm, and (h–k) corresponding to the holographic gratings with a constant-length b = 1.8 μm but dissimilar widths d = 1, 1.4, 1.8, and 2.2 μm, respectively, (g,l) are the fidelities of the attained OV beams as the functions of length b and width d, correspondingly. Reprinted with permission from ref. [152]. Copyright 2016, Elsevier.

Figure 10

(a) Scheme of an OV MEMS Fabry-Perot filter: AR-coating = anti-reflection coating, and DBR = distributed Bragg reflector [160]. (b) Top view of a MEMS tunable Fabry-Perot filter with an integrated SPP [160]. (c) SEM image of a SPP of order l_SPP = 1 on a plane Si substrate [160].

Figure 11

The normalized transversal field component intensity distribution superimposed with polarization map (a,d) [166], Normalized absolute amplitude mapping of dominant E-field component (b,e) and phase distribution of dominant E-field component (c,f) of the quasi-TE (a–c) and quasi-TM (d–f) quasi-degenerate modes of order l = 1 in the symmetric (silica clad) silicon nitride WGs enhanced for phase-matched propagation of the constituent eigenmodes (β₀₁ ≈ β₁₀) [166].

Figure 12

HG-similar mode field allocations in the WG (a–d) [163], WG configuration for concurrently managing l = ±1 OAM mode and l = ±2 OAM mode (e) [163], mode n_eff reliance on WG parameters (f) [163].

Figure 13

Cross-section of rectangular WG coupler (a) [164], the coupling coefficient of TE₁₀ and TE₀₁ modes in case of W = 0.72 µm and H = 0.6 µm (b) [164], the cross-section of cross shape WG coupler (c) [164], the coupling coefficient of TE₁₀ and TE₀₁ modes as a function of t (d) [164].

Figure 14

(a) OAM beam generator principle built on a single-trench WG; (b) A single trench WG in cross-section; (c) Two eigenmodes of a single-trench WG’s field distributions; and (d) For x-polarization, intensity and phase evolutions of a combination of eigenmodes [67].

Figure 15

Detecting OVs: (a) phase of a 13-channel filter; (b) intensity pattern (negative) in the focal plane and correspondence of diffraction orders to OV values; and (c) results of detecting of different OVs in the beam with co-axial superposition exp(−i2φ) + exp(−iφ) (total OAM μ = −0.5) [194].

Figure 16

A diagram of the device’s geometry: (a) Top view of a slot-mode PhC cavity geometry and modeling of the E-field distribution of its fundamental optical mode [212]; and (b) The OAM detector in isometric perspective. The cavity from (a) is attached to the square pad by a hanger whose dimensions w_h and l_h are indicated in (c) [212]. The pad motion is moved to the nanobeam when excited by a source of torque as exhibited by the simulated displacement profile shown in (c) [212].